Development apparatus for continuous rotary electrostatographic apparatus



J1me 30, 1970 Filed Oct. 25. 1965 L. A. TYLER DEVELOPMENT APPARATUS FOR CONTINUOUS ROTARY ELECTROSTATOGRAPHIC APPARATUS 2 Sheets-Sheet 1 Len oq. 1918;". I

United States Patent Olfice 3,517,993 DEVELOPMENT APPARATUS FOR CON- TINUOUS ROTARY ELECTROSTATO- GRAPHIC APPARATUS Len A. Tyler, Evanston, Ill., assignor to Bell & Howell Company, Chicago, 11]., a corporation of Illinois Filed Oct. 23, 1965, Ser. No. 504,037 Int. Cl. G03g 15/08, 15/22 US. Cl. 355-15 Claims This invention relates generally to electrostatographic methods and means and more specifically relates to a de velopment apparatus for a continuous rotary electrostatographic machine wherein the deposition of powder on the image area is controlled as an electrostatic deposition without any mechanical deposition through the utilization of two suitably shaped channels to provide laminar flow of the air streams, one channel supplying the air in which the powder is dispersed, While the other channel supplies the air stream which serves to confine the flow of powder to the development zone and prevent turbulence in the air flow.

One of the problems encountered in practicing electrostatographic techniques in connection with the production of microimages is the development of the electrostatic image with the requisite quality of resolution. Accordingly, it is essential that tears and streaks be avoided and eliminated if at all possible.

In accordance with the principles of the present invention, improvements in the use of air to control the deposition of powder on the image area have been discovered so that the powder deposition occurs electrostatically and without any mechanical deposition.

Thus it is contemplated that a photoconductive image bearing surface be moved in the direction of its length in close proximity to a development surface characterized by successively disposed sections including a fluid entry section for interposing multiple fluid layers between the surfaces, an electrode section for modifying the electrostatic field near the photoconductive surface and a vacuum pickup section for picking up residual development powder.

The fluid entry section is particularly characterized by a pair of independent passages or channels receiving air from a source at increased pressure. One of the channels receives a suspension of a development powder while the other channel carries only clean air. Thus, the clean air stream functions to keep the development powder in the critical areas and to promote laminar flow at the juncture of the powder channel and the development zone. A transition area within each channel changes the configuration of the channel from a substantially symmetrical crosssection to a thin wide configuration at least as thin as the spacing dimension between the confronting surfaces and as wide as the image-bearing surface while providing conditions conducive to laminar flow in the powder stream. Accordingly, the development powder will be deposited on the image area electrostatically and any residual development powder on the exit side of the electrode area will be purged by the vacuum pick-up.

It is an object of the present invention, therefore, to provide improved development means for an electrostatographic apparatus operable in accordance with novel method concepts.

Another object of the present invention is to provide a development unit wherein development powder may be deposited on an image area electrostatically without any mechanical deposition.

A further object of the present invention is to provide improvements in the use of air to control the deposition of powder on an electrostatic image area by providing laminar flow to keep the development powder from being deposited mechanically.

3,517,993 Patented June 30, 1970 A still further object of the present invention is to provide a means of developing electrostatographic images in a continuous rotary apparatus and affording improved resolution characteristics.

Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings in which a preferred structural embodiment of the present invention is shown by way of illustrative example and by means of which the methods of the present invention may be advantageously practiced.

On the drawings:

FIG. 1 is a fragmentary side elevational view of a continuous rotary electrostatographic apparatus utilizing the novel development method and means of the present invention;

FIG. 2 is a fragmentary cross-sectional view taken generally on line 22 of FIG. 1;

FIG. 3 is an enlarged view similar to FIG. 1 but showng additional details of the development unit provided m accordance with the principles of the present invention;

FIG. 4 is a fragmentary cross-sectional view taken on line 4-4 of FIG. 3; and

FIG. 5 is a fragmentary cross-sectional view taken on line 5-5 of FIG. 3.

As shown on the drawings:

A continuous rotary electrostatographic apparatus is shown generally at 10 and includes a rotatable drum 11 coated on its peripheral surface with a photoconductive layer 12 made of a suitable photoconductive material such as selenium. The drum 11 is mounted for rotation on a shaft 13 carried in spaced bearing blocks 14 and 1 6 and driven by a motor 17 through suitable driving connections shown schematically at 18 (FIG. 2).

Outwardly adjacent the drum 11 there is located a plurality of stations for the purpose of elfecting successively the various operations which are characteristic of an electrostatographic reproduction process, namely, charging, exposure, development, transfer, and cleaning. Thus, an ion source is provided to function as a chargmg device and to that end, a corona charging unit may be utilized such as a corotron charging device 19 spaced concentrically adjacent the photoconductive surface 12 and adapted to uniformly charge the photoconductive surface 12 as it is moved past the charging device 19.

The exposure station is established by an optical system including a lens holder 20 by means of which image material to be reproduced is first reduced. The size of the reduction, of course, depends upon the optical characteristics of the optical system and reductions throughout commercial ranges are contemplated, for example, up to 44x. With the image carrier constituting 16 mm. film, a convenient reduction size would be approximately 20 x.

In accordance with the principles of the present invention, a development unit is provided which is shown generally at 21 and there is also provided a transfer station wherein a continuous strip of film such as 16 mm. roll film, shown at 22, is trained over a guide roller 23 carried on a pin 24 supported by a bracket 26. The bracket 26 can be moved towards and away from the drum 11 by means of actuating means shown generally at 27. It will be understood that suitable take-up and drive means for the film 22 are provided.

After the image has been transferred to the film 22, the photoconductive surface 12 is again conditioned for recycling and to that end a cleaning brush 28 is provided, thereby to remove residual developing powder which may remain on the photoconductive surface prior to the sur* face again moving adjacent the charging device 19.

In order to accomplish the improved development of the image in accordance with the invention, a powder cloud generator is employed wherein a powder channel arrangement is incorporated in a development electrode. The output of the powder cloud generator is a dispersion of toner particles in air at relatively high pressure. In order to obtain suitable charging of the powder particles, the powder cloud is discharged through a small bore tube of metal such as stainless steel. The powder suspension that is discharged by that tube is highly turbulent and has a high velocity.

The powder stream in the development zone should be laminar rather than turbulent, of relatively low velocity, and evenly distributed across the width of the zone. The function of the powder channel in the development electrode is to obtain a transition of the powder stream from the conditions existing at the discharge tube to those required in the development zone.

The cross-sectional area of the powder channel at the point at which the powder suspension is discharged from the tube is much larger than that of the tube itself. Consequently, there is a rapid expansion of the air as it leaves the tube, which serves to break up any agglomerates of powder before they reach the development zone. This increase in channel cross-section also acts as a dilfuser and thus slows down the stream from the near sonic velocity in the discharge tube.

The powder suspension then enters the transition zone which serves to distribute the powder in a thin but relatively wide stream, to correspond to the cross-sectional dimensions of the channel formed by the drum and the development electrode. The transition zone also serves to convert the stream from a condition of high turbulence to one of laminar flow.

In order to promote and maintain a condition of laminar flow in the transition and development zones, the following channel characteristics are desirable.

(1) The cross-sectional dimensions of the channel should vary smoothly from inlet to outlet.

(2) The cross-sectional dimensions of the channel near the outlet should approach their final values as nearly asymptotically as possible in order to produce parallel stream lines at the outlet.

(3) The cross-sectional area of the channel should decrease in the direction of flow.

(4) The surfaces of the channel should be smooth and contain no abrupt changes in direction.

Referring now to FIGS. 3-5 in conjunction with FIGS. 1 and 2, it will be noted that the development unit 21 forms one surface of a development zone which surface is of a curvature configuration concentrically complementary to the curvature configuration of the photoconductive surface 12 and spaced from the surface 12 to form therewith a gap or development zone 31 of uniform width and thickness bounded by the surface 30 and the photoconductive surface 12 of the drum 11. Moreover, the surface 30 has a fluid entry section shown generally at 30a for interposing multiple fluid layers into the gap or development zone 31, an electrode section 30b for establishing a bias field adjacent the drum 11 and a vacuum pick-up section 300 for picking up residual development powder. Each of such sections extends through a selected number of degrees of are so that the total extent of the development unit 21 lies adjacent a substantial portion of the photoconductive surface 12 on the drum 11.

Moreover, while the development unit 21 comprises a number of separate surfaces, defining the development zone, as identified at 30a, 30b and 30c, all of the components forming these surfaces are interrelated to effect an essential unity of purpose in promoting the development of very small images without tears and streaks and with good resolution.

As shown in FIG. 3, the development unit 21 has a main body member shown at to which are connected supplemental body members 32 and 33 by means of a plurality of fastener bolts 34.

The main body member 35 has formed therein a dovetail groove 36 receiving a complementary shaped dovetail portion 37 of an electrode 38. The oppositely disposed portion of the electrode 38 is curved to form the corresponding segment 30b of the surface 30. The electrode 38 may be connected to suitable control circuitry in order to establish a bias field in the gap 31 adjacent the photoconductive surface 12.

Multiple fluid layers may be interposed in the gap 31 at the fluid entry section 30a by virtue of the two separate channels formed between the components of the development unit 21 identified by the main body portion 35 and the supplemental body portions 32 and 33.

-A powder cloud generator 40 (FIG. 1) is connected by means of a conduit 42 to a nipple fitting 44. The nipple fitting 44 is connected to a channel 53 by means of an adapter 50 (FIGS. 3 and 5) which threadedly engages the nipple 44 as at 51. The actual discharge of powder-laden air from the nipple 44 occurs through an elongated tube shown at 52 (FIG. 5).

A controlled source of compressed air (not shown) is connected by an elongated tube 41 to a nipple 43. The nipple 43 is connected to adapter 47 as at 48 by means of which air is discharged into a channel 46. The source of compressed air referred to above may also be connected by a tube 62 to a conduit 61 to deliver additional air to the channel 53, if necessary, as described in more detail hereinafter.

Referring now specifically to FIGS. 3 and 4, it will be noted that the configuration of the channel 46 is characterized by an entry portion 46a which is essentially symmetrical, i.e., a uniform geometrical shape such as a circle prescribing a given cross-sectional area.

As shown in FIG. 3, however, the channel 46 tapers convergingly with respect to its height or thickness as shown at 46b, but referring to FIG. 4, it will be noted that in the same transition area, the channel 46 is becoming progressively wider, expanding to a maximum width dimension shown at W which width dimension is wider than the corresponding width of the film strip 22 but is narrower than the total width of the drum 11, thereby to leave a sealing area 54 and a sealing area 56 on opposite sides of the channel 46.

In like manner, the channel 53 also has a symmetrical entry or mouth 53a and a transition area 53b which widens gradually to an exit portion of maximum width shown at X, thereby leaving a sealing area 57 and a sealing area 58 on opposite sides of the channel 53.

The two channels 46 and 53 are spaced from one another so that the channel 53 is actually longer than the channel 46 and has its exit mouth X positioned immediately adjacent the electrode development area portion of the gap 31. Moreover, the channel 53 has an opening 60 connected by means of a conduit 61 and a tube 62 to a controlled source of compressed air, such as the one previously mentioned. Thus, optionally, the dispersion of development powder from tube 52 may be admixed with additional air from channel 61 to control the velocity of the powder suspension in channel 53.

The transition areas in each of the channels 46 and 53 exhibit the characteristics of uniformly varying cross-sectional area chosen to provide laminar flow while changing the cross-sectional shape of the channel from essentially square to that of the development zone. In other words, the thickness of the slot or channel thins down corresponding to the widening of the transition area in such a manner that the flow tends to remain laminar.

Moreover, the channel 46 which carries a stream of clean air discharges into the gap 31 at a point upstream of the discharge of the development powder, thereby increasing the pressure on the upstream side of the gap 31 and thereby preventing the development powder from backing up and leaving the electrode area of the gap 31 through the entrance or upstream side of the gap 31.

The development powder may conveniently take the form of a particulated material such as carbon particles ground to a requisite degree of fineness. By choosing the material of which tube 52 is fabricated, the particulate material will acquire a suitable triboelectric charge and be attracted to the charge pattern appearing on the photoconductive surface 12 and will render such charge pattern visible as a developed microimage.

In order to recover unused particulate material, the vacuum pick-up portion 300 is provided in the development unit 21 with a fitting as shown generally at 64 and has a hollow interior 66 with a vacuum slot 67 opening into the development zone 31 adjacent the downstream end of the electrode area. An extension of the surface 30 is formed by an offset portion 68 which provides the surface 300. The hollow interior 66 is communicated to a suitable source of vacuum by means of a conduit 69 connected to a tube 70 (FIG. 1).

The surface of the electrode may be kept clean by means of a reciprocating mechanism not herein disclosed, and a pair of independently rotatable burshes 70 and 71 are provided on opposite sides of the drum 11 to engage the surface 30b of the electrode during the course of its reciprocation. The brushes are driven by means of a pulley drive shown at 72 and 73.

To further identify the characteristics of the transition areas provided in accordance with this invention a typical transition zone, as illustrated in FIG. 5, may be characterized by dimensional proportions of the following order as indicated at locations identified by letter legends (a)-(g),,inclusive:

The Reynolds numbers (NR) are calculated on the basis of a 90 p.s.i. pressure in the powder cloud generator and 3.6 cubic feet/hour flow and a needle size corresponding to a #22 hypodermic needle. (NR) at the exit of tube 52 is 8,240.

In operation, the entire process is carried out in a continuous manner. Thus, the drum may be rotated in a counterclockwise direction, using the orientation of FIG. 1, and the photoconductive surface 12 will be successively uniformly charged by the charging device 19 and exposed when positioned oppositely the optical system 20 and then developed by the development unit 21. It will be understood that the continuous flow apparatus shown generally at may include a light-tight enclosure 10a so that the optical exposure may be effected in darkness.

Multiple layers of fiuid are interposed in the development zone between the development unit 21 and the photoconductive surface 12. In this connection, two channels 46 and 53 are provided, the channel 53 functioning as a carrier stream to interpose a fluid layer containing developer powder into the development zone between the electrode 38 and the photoconductive surface 12. A stream of clean air discharge from the channel 46 will prevent the developer powder from leaving the electrode area via the entrance or upstream side of the gap 31. The extremely close clearance relation between the photoconductive surface 12 and the sealing areas 54, 56 and 57, 58, will confine the developer powder in the developer zone. The developer powder is deposited on the image area, thereby rendering the image visible and the image is then transferred to the surface of the film 22 by pressure contact regulated by the actuator means 27.

To prevent unwanted deposition in area 300, unused particulate material is removed from the situs through a vacuum slot 67, the tube 70 and the conduit 69 to a suitable collection zone.

The photoconductive surface 12 is cleaned by a brush 28, thereby conditioning the photoconductive surface 12 for a new cycle. The electrode 38 is similarly cleaned and conditioned for the next cycle by the brushes 70 and 71.

Although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon, all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. In a xerographic apparatus having a rotatable drum,

a photoconductive peripheral surface formed thereon,

drive means for rotating said drum,

means forming charging and exposing stations adjacent said drum for forming an electrostatic image as a charge pattern on said photoconductive surface, and development means adjacent said drum to form a visible image corresponding to said charge pattern, said development means comprising a development electrode having a curved surface spaced in closely confronting relation to said peripheral surface to modify the development field, the improvement comprising:

closed passage means for interposing two independent layers of fluid in said field, means for conducting air from a source at increased pressure into said passage means, and tubular means for dispersing developer powder in a first of said layers, said first layer being introduced into said field downstream from a second of said layers,

said second layer operating to prevent developer powder from leaving said field, each said passage means further characterized as having an inlet substantially symmetrical in geometric configuration, a transition zone gradually tapering divergently in width dimension and convergently in thickness dimension and an outlet which is at least as thin as and at least as wide as the development zone between the photoconductive surface and the electrode area, thereby to deposit the developer powder on the surface in the configuration of the charge pattern and insure laminar flow of the combined layers through the development field.

2. Apparatus for controlling the deposition of particulate material electrostatically comprising,

means forming an electrostatically chargeable surface,

an electrode disposed in closely spaced relation to said surface and together therewith forming a confined zone,

means forming a first closed channel for directing a powder cloud stream from a source at increased pressure into said zone,

means forming a second closed channel upstream of said first closed channel for directing a stream of clean air adjacent the powder cloud stream, thereby increasing the pressure at one side of the channel to prevent the particles from leaving the electrode area, from said one side,

each of said channels having an inlet substantially symmetrical in geometric configuration, a transition area wherein the channel gradually widens without any abrupt dimensional or directional changes to at least the width of the image area while the thickness of said channel gradually thins down correspondingly, without any abrupt dimensional or directional changes, and an outlet which is thin and wide, thereby to convert the stream from a condition of turbulence to one of laminar flow.

3. Apparatus of claim 2 wherein said transition area is further characterized in that the cross-sectional area decreases in the direction of flow of said stream and the final dimensions of said cross-section are approached substantially asymptotically.

4. A development unit for an electrostatographic drum, comprising,

means forming a surface within a development zone of a curvature configuration substantially the same as the drum and forming with the photoconductive surface of the drum a development zone of uniform width and thickness concentrically disposed with respect to the axis of the drum,

said surface having a fluid entry section for interposing multiple fluid layers into said zone, an electrode section for modifying the bias field adjacent the drum, and a vacuum pick-up section for picking up residual development powder, said fluid entry section being particularly characterized by having two independent closed passage means formed therein and means for receiving air therein from a source at increased pressure,

one of said passage means having means for dispersing a developer powder in the fluid layer as a carrier stream, the other passage means having an opening formed in said surface upstream of said first mentioned passage means to assist in directing the flow of developer powder through said zone, and each of said passage means further characterized as being formed to include a transition zone having an inlet substantially symmetrical in geometric configuration and smoothly and gradually tapering divergently in width dimension and convergently in thickness dimension to form an outlet which is thin and wide whereby to insure laminar How of the fluid layer through the development fields.

*5. Apparatus of claim 4 wherein said transition zone is further characterized in that the cross-sectional area decreases in the direction of flow of said stream and the final dimensions of said cross-section are approached substantially asymptotically.

References Cited UNITED STATES PATENTS 2,808,023 10/1957 Hayford 11717.5 X 2,842,456 7/1958 Carlson 1l717.5 2,872,338 2/1959 Landrigan et al 117--17.5 2,918,900 12/1959 Carlson ll8637 2,942,573 6/1960 Crumrine 1l717.5 X 2,965,069 12/ 1960 Hayford et al 118-637 3,176,653 4/ 1965 Hansen 118-637 3,251,685 5/1966 Bickmore 11717.5 X 3,369,918 2/1968 Young 117-37 3,129,115 4/1964 Clark 118637 3,157,546 11/1964 Cover 951.7 X 3,045,644 7/ 1962 Schwertz 118637 3,102,045 8/ 1963 Metcalfe 117--37 3,229,603 1/ 1966 Boschet 951.7

WILLIAM D. MARTIN, Prmary Examiner E. J. CABIC, Assistant Examiner US. Cl. X.R. 

1. IN AN XEROGRAPHIC APPARATUS A ROTATABLE DRUM, A PHOTOCONDUCTIVE PERIPHERAL SURFACE FORMED THEREON, DRIVE MEANS FOR ROTATING SAID DRUM, MEANS FORMING CHARGING AND EXPOSING STATIONS ADJACENT SAID DRUM FOR FORMING AN ELECTROSTATIC IMAGE AS A CHARGE PATTERN ON SAID PHOTOCONDUCTIVE SURFACE, AND DEVELOPMENT MEANS ADJACENT SAID DRUM TO FORM A VISIBLE IMAGE CORRESPONDING TO SAID CHARGE PATTERN, SAID DEVELOPMENT MEANS COMPRISING A DEVELOPMENT ELECTRODE HAVING A CURVED SURFACE SPACE IN CLOSELY CONFRONTING RELATION TO SAID PERIPHERAL SURFACE TO MODIFY THE DEVELOPMENT FIELD, THE IMPROVEMENT COMPRISING: CLOSED PASSAGE MEANS FOR INTERPOSING TWO INDEPENDENT LAYERS OF FLUID IN SAID FIELD, MEANS FOR CONDUCTING AIR FROM A SOURCE AT INCREASED PRESSURE INTO SAID PASSAGE MEANS, AND TUBULAR MEANS FOR DISPERSING DEVELOPER POWDER IN A FIRST OF SAID LAYERS, SAID FIRST LAYER BEING INTRODUCED INTO SAID FIELD DOWNSTREAM FROM A SECOND OF SAID LAYERS, SAID SECOND LAYER OPERATING TO PREVENT DEVELOPER POWDER FROM LEAVING SAID FIELD, EACH SAID PASSAGE MEANS FURTHER CHARACTERIZED AS HAVING AN INLET SUBSTANTIALLY SYMMETRICAL IN GEOMETRIC CONFIGURATION, A TRANSITION ZONE GRADUALLY TAPERING DIVERGENTLY IN WIDTH DIMENSION AND CONVERGENTLY IN THICKNESS DIMENSION AND AN OUTLET WHICH IS AT LEAST AS THIN AS AND AT LEAST AS WIDE AS THE DEVELOPMENT ZONE BETWEEN THE PHOTOCONDUCTIVE SURFACE AND THE ELECTRODE AREA, THEREBY TO DEPOSIT THE DEVELOPER POWDER ON THE SURFACE IN THE CONFIGURATION OF THE CHARGE PATTERN AND INSURE LAMINAR FLOW OF THE COMBINED LAYERS THROUGH THE DEVELOPMENT FIELD. 